The present disclosure relates to an environmental control system, and more specifically, to methods and systems for providing external air and recirculated air to an aircraft.
Traditionally, pressurized aircraft use Environmental Control Systems (“ECS”) to maintain cabin pressurization and to control cabin temperatures during flight. Due to high occupant density in an aircraft cabin, a common approach for an ECS is to flow external air from the engines to pressurize the cabin. This air supply is known as ‘bleed air’. Some known systems use this ducted bleed air, cool the bleed air using air conditioning packs and then mix the bleed air with recirculated cabin air flow for resupply into the cabin and the flight deck during flight condition. On the ground, aircraft typically operate a smaller compressor known as an auxiliary power unit to bleed external air for pressurizing cabin air. In some known aircraft, the recirculated air flow may provide about 50% of total air flow and the external bleed air may provide about 50% of total air flow.
More particularly, in order to maintain cabin pressurization and temperature in some known aircraft, external air is supplied to the cabin via air conditioning packs and a portion of the air in the cabin is recirculated by recirculation fans to provide an acceptable level of volumetric airflow to the aircraft passengers. In many cases, recirculation fans run at a constant speed and the total volumetric airflow to the cabin can be maintained constant by modulating the flow provided by the air conditioning packs. In some cases, air recirculation is passed through a filter to improve cabin air quality. In other cases, aircraft include cabin humidifiers and/or dehumidifiers to further condition the cabin air.
In recent years, due to increased passengers travelling by air annually worldwide, there are increased concerns, regulations and needs regarding the improvement of cabin air quality and fuel saving for commercial air travel. As the amount of external air provided by the ECS increases, aircraft fuel efficiency is reduced, and in particular when the ECS uses bleed air from the aircraft engines. Accordingly, it can be desirable to reduce the amount of external air flowing into the cabin while meeting governmental regulations that may require a minimum flow rate per occupant during flight. Moreover, an ECS that improves airflow and air quality in the cabin; reduces CO2 and other pollutants in the cabin; reduces thermal loading of the aircraft; reduces external air input and increases fuel savings is desired.